The Placebo Effect

In my post on warm milk and sleepiness - the dairy acts like a placebo - a commenter made an astute point:

what does "placebo" mean in that context? If you have developed the pathways that insist on Warm Milk = Time to Sleep, that effect is very real...

Whether purely conditioned, or based on some real effect we still don't understand...is seems to me to go beyond what we typically called placebo.

Was Pavlov's dog suffering from Placebo effect each time he salivated?

From the perspective of the brain, the placebo effect is simply a specific pattern of brain changes that make us feel better. Differentiating these brain changes from non-placebo medical interventions can be a tricky business. (For example, scientists estimate that 80 percent of the effectiveness of Prozac is due to the placebo effect.) The fact of the matter is that we can change ourselves: every thought is embodied as a set of biochemical alterations in the cortex. When a person feels better, nobody knows if it's these optimistic thoughts or the drug itself that are responsible for the improvement.

How does the placebo effect work? Tor Wager, a neuroscientist at Columbia University, gave people painful electrical shocks while they were stuck in an fMRI machine. Half of the subjects were then supplied with a fake pain-relieving cream. As expected, people given the pretend cream said the shocks were significantly less painful. The placebo effect eased their suffering. Wager then imaged the specific parts of the brain that controlled this psychological process. When people were told that they'd just received a pain-relieving cream, their prefrontal cortex responded by inhibiting the activity of the emotional brain areas (like the insula) that normally respond to pain. (Further research suggests that the brain releases endogenous opioids.) However, when the same people were informed that the same cream was "ineffective" at blocking pain, their prefrontal cortex went silent. Because people expected to experience less pain, they ended up experiencing less pain. Their predictions became self-fulfilling prophecies.

What I find most interesting about this experiment is that lots of scientists are currently trying to develop a drug (like D-Cycloserine) that will imitate the real cortical effects of the placebo effect, and reduce the activity of emotional areas (like the insula and anterior cingulate) that respond to pain. So we'll end up having to pay lots of money for a pharmaceutical painkiller (that probably has some side-effects) when we can get similar palliative benefits just from thinking good thoughts. (I've written about some doctors who are trying to harness our conscious thoughts here.)

My only problem with the placebo effect is that it's got such a bad reputation. (We forget, of course, that until the 20th century almost all medicine was nothing but the placebo effect.) When it comes to fixing the brain, thinking that we've been fixed is often medicine enough.

For more on the placebo effect, check out Radio Lab.